1. Field of the Invention
The present invention pertains to the field of personal computer systems. More particularly, this invention relates to a multifunction input/output subsystem for a personal computer that enables unrestricted sound file input and output through a telephone set.
2. Art Background
Non dedicated telephone lines are often employed in small office or home office environments to provide modem and fax communication lines for a personal computer. The personal computer typically employs a non dedicated telephone line for sharing modem and fax calls as well as voice calls. Such telephone line sharing enables modem and fax communication while avoiding the cost of providing separate modem telephone lines and fax telephone lines in the small business or home office.
In such small business or home office environments, a telephony subsystem of the personal computer typically performs the telephone line interface functions required for modem, fax and voice communication. The telephone line interface functions include line seizure and ring detect, as well as audio and digital signal processing functions.
Typically, application programs executing on the personal computer perform the higher level modem, fax and voice communication functions as well as user interface functions.
In a typical small business or home office telephone line topology, the telephony subsystem is coupled to an incoming telephone line or a private branch exchange (PBX) line. The telephony subsystem usually drives one or more serial telephones over a local line.
Typically in such systems, the telephony subsystem transfers incoming voice calls on the telephone line to the serial telephone over the local line to enable a user to receive the voice call. The telephony subsystem usually employs a switching device such as a relay to couple the telephone line to the local line and serial telephone.
Unfortunately is such prior systems, the telephony subsystem creates a physical connection through the relay between the telephone line and the local line to transfer incoming voice calls to the serial telephone. With such a physical connection, the originator of the incoming voice call hears a busy signal over the telephone line if the serial telephone is off-hook during the incoming call. As a consequence, the serial telephone must remain on-hook to receive incoming voice calls, thereby precluding the use of the serial telephone for other input/output functions.